Viscose method

Finally, in 1894, Charles Frederick Cross, Edward John Bevan, and Clayton Beadle patented their artificial silk, which they named "viscose", because the reaction product of carbon disulfide and cellulose in basic conditions gave a highly viscous solution of xanthate. Avtex Fibers Incorporated began selling their formulation in 1910 in the United States.
The name "rayon" was adopted in 1924, with "viscose" being used for the viscous organic liquid used to make both rayon and cellophane. In Europe, though, the fabric itself became known as "viscose," which has been ruled an acceptable alternative term for rayon by the U.S. Federal Trade Commission.
The method is able to use wood (cellulose and lignin) as a source of cellulose while the other methods need lignin-free cellulose as starting material. This makes it cheaper and therefore it was used on a larger scale than the other methods.

Contamination of the waste water by carbon disulfide, lignin and the xanthates made this process detrimental to the environment. Rayon was only produced as a filament fiber until the 1930s when it was discovered that broken waste rayon could be used in staple fiber.

The physical properties of rayon were unchanged until the development of high-tenacity rayon in the 1940s. Further research and development led to the creation of high-wet-modulus rayon (HWM rayon) in the 1950s .

Major fiber properties

Rayon is a very versatile fiber and has the same comfort properties as natural fibers. It can imitate the feel and texture of silk, wool, cotton and linen. The fibers are easily dyed in a wide range of colors. Rayon fabrics are soft, smooth, cool, comfortable, and highly absorbent, but they do not insulate body heat, making them ideal for use in hot and humid climates .

The durability and appearance retention of regular rayon are low, especially when wet; also, rayon has the lowest elastic recovery of any fiber. However, HWM rayon is much stronger and exhibits higher durability and appearance retention. Recommended care for regular rayon is dry-cleaning only; HWM rayon can also be machine washed .

Gallery of textures

Physical structure of rayon

Regular rayon has lengthwise lines called striations and its cross-section is an indented circular shape. The cross-sections of HWM and cupra rayon are rounder. Filament rayon yarns vary from 80 to 980 filaments per yarn and vary in size from 40 to 5000 denier. Staple fibers range from 1.5 to 15 denier and are mechanically or chemically crimped. Rayon fibers are naturally very bright, but the addition of delustering pigments cuts down on this natural brightness .

Production method

Regular rayon (or viscose) is the most widely produced form of rayon. This method of rayon production has been utilized since the early 1900s and it has the ability to produce either filament or staple fibers. The process is as follows:

Xanthation: The aged "white crumb" is mixed with carbon disulfide in a process known as , the aged alkali cellulose crumbs are placed in vats and are allowed to react with carbon disulphide under controlled temperature (20 to 30°C) to form cellulose xanthate. (C6H9O4ONa)n + nCS2 ----> (C6H9O4O-SC-SNa)n

Yellow Crumb: Xanthation changes the chemical makeup of the cellulose mixture and the resulting product is now called "yellow crumb"

Viscose: The "yellow crumb" is dissolved in a caustic solution to form viscose

Ripening: The viscose is set to stand for a period of time, allowing it to ripen

Filtering: After ripening, the viscose is filtered to remove any undissolved particles

Degassing: Any bubbles of air are pressed from the viscose in a degassing process

Extruding: The viscose solution is extruded through a spinneret, which resembles a shower head with many small holes

Acid Bath: As the viscose exits the spinneret, it lands in a bath of sulfuric acid resulting in the formation of rayon filaments

Drawing: The rayon filaments are stretched, known as drawing, to straighten out the fibers

Washing: The fibers are then washed to remove any residual chemicals

Cutting: If filament fibers are desired the process ends here. The filaments are cut down when producing staple fibers

High Wet Modulus rayon (HWM) is a modified version of viscose that has a greater strength when wet. It also has the ability to be mercerized like cotton. HWM rayons are also known as "polynosic" or can be identified by the trade name Modal .

High Tenacity rayon is another modified version of viscose that has almost twice the strength of HWM. This type of rayon is typically used for industrial purposes such as tire cord .

Cupramonium rayon has properties similar to viscose but during production, the cellulose is combined with copper and ammonia (Schweizer's reagent). Due to the environmental effects of this production method, cupramonium rayon is no longer produced in the United States .

Producers

Trade names are used within the rayon industry to determine the type of rayon used.

Bemberg, for example, is a trade name for cupramonium rayon developed by J.P. Bemberg that is now only produced in Italy due to EPA regulations in the US .